Glaucoma is a heterogeneous group of optic neuropathies that share certain clinical features. The loss of vision in glaucoma is due to the selective death of retinal ganglion cells in the neural retina that is clinically diagnosed by characteristic changes in the visual field, nerve fiber layer defects, and a progressive cupping of the optic nerve head (ONH). One of the main risk factors for the development of glaucoma is the presence of ocular hypertension (elevated intraocular pressure, IOP). An adequate intraocular pressure is needed to maintain the shape of the eye and to provide a pressure gradient to allow for the flow of aqueous humor to the avascular cornea and lens. IOP levels may also be involved in the pathogenesis of normal tension glaucoma (NTG), as evidenced by patients benefiting from IOP lowering medications. Once adjustments for central corneal thickness are made to IOP readings in NTG patients, many of these patients may be found to be ocular hypertensive.
The elevated IOP associated with glaucoma is due to elevated aqueous humor outflow resistance in the trabecular meshwork (TM), a small specialized tissue located in the iris-corneal angle of the ocular anterior chamber. Glaucomatous changes to the TM include a loss in TM cells and the deposition and accumulation of extracellular debris including proteinaceous plaque-like material. In addition, there are also changes that occur in the glaucomatous ONH. In glaucomatous eyes, there are morphological and mobility changes in ONH glial cells. In response to elevated IOP and/or transient ischemic insults, there is a change in the composition of the ONH extracellular matrix and alterations in the glial cell and retinal ganglion cell axon morphologies.
Primary glaucomas result from disturbances in the flow of intraocular fluid that has an anatomical or physiological basis. Primary open angle glaucoma (POAG), also known as chronic or simple glaucoma, represents ninety percent of all primary glaucomas. POAG is characterized by the degeneration of the trabecular meshwork, resulting in abnormally high resistance to fluid drainage from the eye. A consequence of such resistance is an increase in the IOP that is required to drive the fluid normally produced by the eye across the increased resistance.
Histopathologic studies of the glaucomatous optic nerve head in POAG reveal astroglial activation and tissue remodeling, which accompanies neuronal damage. As a part of tissue remodeling, backward bowing and disorganization of the laminar cribriform plates are common characteristics of glaucomatous eyes with either normal or high IOP. These histologic changes are accompanied by the upregulation of extracellular matrix components including collagen and proteoglycan, and adhesion molecules by optic nerve head astrocytes in glaucomatous eyes. The astroglial activation seen in glaucomatous optic nerve heads likely represents an attempt to limit the extent of the injury and promote the tissue repair process. However, despite the astroglial activation, there is limited deposition of extracellular matrix in glaucomatous optic nerve atrophy, which does not retain characteristics of scar tissue formation. This suggests that there are diverse cellular responses to the initial event or subsequent tissue injury, which preferentially results in tissue degradation.
Open angle glaucoma (OAG) the second led cause of irreversible blindness in the United States, comprises 2 major syndromes: pi open angle glaucoma (PiOAG) and normal pressure glaucoma (NPG). PiOAG is a disease generally characterized by a clinical triad which consists of 1) elevated IOP; 2) the appearance of optic atrophy presumably resulting from elevated IOP; and 3) a progressive loss of peripheral visual sensitivity in the early stages of the disease, which may ultimately progress and impair central visual acuity (Quigley, 1993, New Engl J Med 328:1097-1106.) Studies have indicated, however, that a surprisingly high percentage of patients with OAG have findings identical to those in PiOAG, but with a singular exception; namely, that the IOP has never been demonstrated to be elevated. Several large population-based studies have documented the high prevalence of this form of glaucoma, often called “low tension glaucoma” (but more accurately called NPG. The most conservative of these estimates place the percentage of glaucoma that occurs in the presence of “normal” IOP at approximately 20-30% (Sommer, 1989, Am J. Ophthalmol. 107:186-188; and Sommer, 1996, Eye 10:295-301).
In addition to the most common forms of glaucoma described above, there are secondary and closed angle forms of glaucoma, which typically result in elevated IOP due to a variety of mechanisms. In virtually all these other forms of glaucoma, elevated eye pressure is found, and a characteristic optic neuropathy similar to that found in OAG ensues. If untreated, elevated intraocular pressure in these glaucomas invariably leads to visual loss and eventual blindness. In many forms of glaucoma, including those with normal IOP, lowering of IOP often fails to halt the progression of the disease. Comparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressures (Collaborative Normal-Tension Glaucoma Study Group, 1998, Am J. Ophthalmol. 126:487-97).
Current anti-glaucoma therapies include lowering IOP by the use of suppressants of aqueous humor formation or agents that enhance uveoscleral outflow, laser trabeculoplasty, or trabeculectomy, which is a filtration surgery to improve drainage. Pharmaceutical anti-glaucoma approaches have exhibited various undesirable side effects. For example, miotics such as pilocarpine can cause blurring of vision and other negative visual side effects. Systemically administered carbonic anhydrase inhibitors (CAIs) can also cause nausea, dyspepsia, fatigue, and metabolic acidosis. Further, certain beta-blockers have increasingly become associated with serious pulmonary side effects attributable to their effects on beta-2 receptors in pulmonary tissue. Sympathomimetics cause tachycardia, arrhythmia and hypertension. Such negative side effects may lead to decreased patient compliance or to termination of therapy. In addition, the efficacy of current IOP lowering therapies is relatively short-lived requiring repeated dosing during each day and, in some cases, the efficacy decreases with time.
In view of the importance of glaucoma, and the inadequacies of prior methods of treatment, it would be desirable to have an improved method of treatment.
Tumor necrosis factor α (TNFα) is a major mediator of the inflammatory response, and has been implicated in many human diseases. Binding of TNFα to its cell surface receptor, TNF receptor-1 (TNFR1), activates a signaling cascase affecting a wide variety of cellular responses, including apoptosis and inflammation. TNFα itself is initially expressed as an inactive, membrane-bound precursor. Release of the active form of TNFα from the cell surface requires proteolytic processing of the precursor by TNFα converting enzyme (TACE/ADAM17). Inhibiting expression of TNFR1, TACE, or both will effectively reduce the action of TNFα.
In addition, studies have implicated TNFα signaling in the disease process in glaucoma. Retinal ganglion cells are susceptible to TNFα-induced apoptosis (Fuchs et al., 2005, Invest. Ophthalmol. Vis. Sci. 46:2983-2991). Expression of TNFα and its receptor, TNFR1, is increased in glaucomatous eyes (Tezel et al., 2001, Invest. Ophthalmol. Vis. Sci. 42:1787-1794; Yuan et al., 2000, Glia 32:42-50; Yan et al., 2000, Arch. Ophthalmol. 118:666-673). In addition, U.S. Pat. No. 6,531,128 showed increased expression of TNFα and TNFR1 in glaucomatous optic nerve head and retina, suggesting a role for TNFα in the neurodegenerative process of glaucoma. In response to simulated ischemia and increased hydrostatic pressure, glial cells secrete TNFα and facilitate the apoptotic death of co-cultured retinal ganglion cells (Tezel et al., 2000, J. Neurosci. 20:8693-8700). Polymorphisms in the TNFα promoter are associated with increased risk for glaucoma (Lin et al., 2003, Eye 17:31-34; Funayama et al., 2004, Invest. Ophthalmol. Vis. Sci. 45:4359-4367). Thus, interfering with TNFα signaling is desirable to protect retinal ganglion cells from transient increases in intraocular pressure (IOP), and for treating and/or preventing elevated IOP.
The present invention addresses the above-cited ocular pathologies and provides compositions and methods using interfering RNAs that target TACE and/or TNFR1 for treating ocular conditions associated with elevated IOP, such as glaucoma. U.S. Patent Publication 2005/0227935, published Oct. 13, 2005, to McSwiggen et al. relates to RNA interference mediated inhibition of TNF and TNF receptor gene expression. However, said publication teaches none of the particular target sequences for RNA interference as provided herein.